Vacuum degasifying apparatus



P 3, 1969 TAKAHO KAWAWA 3,468,525

VACUUM DEGASIFYING APPARATUS Filed Nov. 15, 1966 2 Sheets-Sheet 1 FIG. 9 48 Twewgw W INVENTOR.

BY W

Sept. 23, 1969 Filed Nov. 15. 1966 FIG. 5

TAKAHO KAWAWA VACUUM DEGASIFYING APPARATUS 2 Sheets-Sheet 2 l khvwura INVEIVTOR.

BY (W United States Patent 3,468,525 VACUUM DEGASIFYING APPARATUS Takaho Kawawa, Tokyo, Japan, assignor to Nippon Kokan Kabushiki Kaisha, Tokyo, Japan, a corporation of Japan Filed Nov. 15, 1966, Ser. No. 594,567 Claims priority, application Japan, Nov. 16, 1965, 40/ 70,106 Int. Cl. C21c 7/10 US. Cl. 266-434 1 Claim ABSTRACT OF THE DISCLOSURE A continuous degasifying apparatus wherein a vacuum vessel is disposed over a ladle containing molten metal. The vessel is rotatably supported so it can rotate about a vertical axis. The vacuum vessel has a cylindrical tail extending down into the ladle. Molten metal is drawn up from the ladle through a draw-up conduit and thrown out by centrifugal force and returned to the ladle through a discharge conduit having an opening towards the periphery of the vacuum vessel. The discharge conduit passes through the tail down into the ladle along the axis of rotation.

The present invention relates to a vacuum degasifying apparatus to remove gases harmful to a required metallic structure from molten metal, and in particular to vacuum degasifiers of forced circulation type which operate by forcibly circulating molten metal between a vacuum vessel and a ladle to remove gases contained in the molten metal within the vacuum vessel.

The prior-art vacuum degasifying apparatus falls into two types; namely, vacuum up-down motion type and vacuum forced circulation type, The first mentioned type was developed by Dortmund-Herder Hiittenunion AG. in Germany in 1965 and operated by immersing a single pipe extending from the bottom of a vacuum vessel into molten metal contained in a ladle and exhausting the vessel to draw up molten metal into the evacuated vessel to eifect gas removal, and repeating the above process by vertically moving either the vacuum vessel or the ladle at a suitable period of time to shift molten metal so as to gradually subject the entire charge of molten metal in the ladle to the degasifying treatment. With this method it is indispensable to vertically move either the vacuum vessel or the ladle, which requires a large hydraulic or oil-pressure equipment to increase installation and maintenance costs. Further, the actual degasifying treatment within the vac uum vessel is done only when molten metal is being sucked up in the vacuum vessel, which amounts merely to a half of the entire working time to result in a low rate of operation.

The second type was introduced into the industry by Ruhr Stahl in Germany in 1956 and operated by immersing two pipes extending from the bottom of a vacuum vessel into molten metal contained in a ladle, and then continuously exhausting the vessel and at the same time directing molten metal from the ladle through the one pipe to the reduced-pressure vessel by blowing up argon gas from the lower end of this pipe while returning it from the vessel through the other pipe to the ladle to effect gas removal. With this method the rate of operation is enhanced as compared to the previous type since the degasifying treatment is continuously made. However, with such a method a high degree of vacuum is hardly attained because of the blowing up of argon gas through one of the pipes to force circulation of molten metal. Further, there is a possibility of circulating only a portion of the molten metal in the ladle to leave the rest of molten metal not degasified.

The primary object of this invention is to provide a continuous vacuum degasifying apparatus which permits control of speed of circulation of molten metal and affords a high rate of operation.

Another object of this invention is to provide a continuous vacuum degasifying apparatus where the open ings of circulation conduits open to the inside of the ladle are arranged in such a manner that favorable circulation of molten metal may be attained.

The invention will be more clearly understood from the following description of a preferred embodiment of the continuous vacuum degasifying apparatus with reference to the accompanying drawings, in which:

FIG. 1 is a front elevation, partly in section, of a preferred embodiment of the continuous vacuum degasifying apparatus according to this invention;

FIG. 2 is a section taken along line Il-II of FIG. 1;

FIG. 3 is a section taken along line IIL-III of FIG. 1;

FIG. 4 is a section taken along line IV-IV of FIG. 1; and

FIG. 5 is a section taken along line VV of FIG. 2.

Referring now to the drawings, the reference numeral 1 designates a carriage supported on rails 2 by means of wheels 3. The carriage 1 carries a ladle 4 which contains molten metal indicated at a whose free surface is covered with powdery sealing agent indicated at b floating on the molten metal for heat insulation and prevention of exposure to atmosphere of the molten metal. The rails 2 are secured to a movable floor member 5 which may be lifted to the operative position as shown in FIG. 1 by means of, for instance, pist0n-cyliuder assemblies 6 provided therebelow in the operation of the degasifying apparatus and which otherwise is lowered to such position that the rails 2 are aligned with rails not shown on a stationary floor. When the floor member 5 is in the lowered position the ladle 4 is conveyed to a position direcly beneath a refractory-lined vacuum vessel 7 which is supported in a frame structure 8 built over the horizontal passage of the ladle 4. The frame structure 8 is provided with a circular rail 9 disposed horizontally and directly above the movable floor member 5, The vacuum vessel 7 is provided with a plurality of suspenders 10 secured thereto, each having a radial pin shaft 11 rotatably carrying a wheel 12 which is supported on and adapted to revolve over the circular rail 9. The vacuum vessel 7 is provided with a large wheel gear 13 concentric with the circular rail 9 and meshing with a pinion gear 14 secured to a drive shaft 15a of a motor 15 for rotation of the vacuum vessel 7. The motor 15 may be driven to rotate the vacuum vessel 7 at a desired speed. The vacuum vessel 7 has a neck 7a which is provided at its upper end with a disk 17a which defines together with another disc 17b in sealing contact with the lower disc 17a an annular gas passage 16, the discs 17a and 17b constituting a frictional seal mechanism 17. The upper disc 17b is secured to a tube 20 the upper end of which is in turn secured to a cross beam lattice 18 at the top of the frame structure 8. The tube 20 has a branch 21 leading to a vacuum pump not shown. A gas pumping-up passage formed by the branch tube 21 and the vertical tube 20 passes through the discs 17a and 17b and the neck 7a, and communicates with the interior of the vacuum vessel '7. The annular gas passage 16 formed in the frictional seal mechanism 17 communicates with an end of a pipe 22 threadedly secured to the upper disc 17b and leading to a gas supplying source not shown. The annular gas passage 16 also communicates with an end of a gas supplying pipe 23 threadedly secured to the lower disc 17a to downwardly extend along the outer surface of the vacuum vessel 7 and bent back to pass through the bottom of the vacuum vessel 7. The vacuum vessel 7 has a cylindrical tail 7b downwardly extending from its bottom and concentric with the axis of its rotation. As is best apparent from FIG. 3, the tail 7b consists of a refractory member formed with a central molten metal discharge conduit 24 and two molten metal draw-up conduits 25 symmetrical with respect to the central discharge conduit 24. A metal sleeve is mounted on the cylindrical refractory member to provide mechanical strength to the tail 7b. The discharge conduit 24 is open at the lower end of the tail 7b, while the draw-up conduits 25 have their respective openings located at a certain distance above the lower end of the tail 7 b. The draw-up conduits 25 extend vertically upward through a bottom refractory member and are open to the interior of the vacuum vessel 7 at substantially central portions of the bottom member while the discharge conduit 24- divides into two radial branch conduits cut in the bottom member and open to the interior of the main barrel at portions of the bottom member substantially adjacent to inner peripheral walls of the main barrel, as most clearly seen from FIG. 3. As shown in FIGS. 2 and 5, the bottom member is formed with a hole 26 which communicates with the end of the gas supplying pipe 23 and which is filled with porous refractory brick 27. The reference numeral 28 in FIG. 1 indicates a valve normally sealing a hopper 19 which may be charged with a suitable filling material to be spattered onto molten metal in the vacuum vessel 7. An invertedfunnel-shaped member 29 is suspended from the center of the ceiling of the vacuum vessel for the purpose of dispersing the filling material to be filled in the molten metal and at the same time preventing the splashing and accumulation of molten metal introduced into the vacuum vessel 7 on the open end of the gas pumping passage to choke the same.

In operation, the carriage 1 supporting the ladle 4 filled with molten metal is first transported to the rails 2 on the movable floor member 5 positioned directly beneath the vacuum vessel 7. Then under the action of the pistoncylinder assemblies 6 the movable floor member 5 together with the carriage 1 supporting the ladle 4 is vertically raised to a position shown in FIG. 1 to immerse the tail 7b of the vacuum vessel 7 in molten metal contained in the ladle 4. When the position of the ladle 4 as shown in FIG. 1 has been reached, the motor is operated to rotate the vacuum vessel 7 through the wheel and pinion gears 13 and 14, while concurrently operating a vacuum pump to reduce pressure in the vacuum vessel 7. At first, the molten metal in ladle 4 is drawn up in the vacuum vessel through both conduits 24 and 25. This is only when the barometric level in the vacuum vessel is first lowered. However, because of the rotation of the vacuum vessel, the molten metal in the vacuum vessel is subject to movement towards the peripheral walls of the vessel so that it is thrown out through conduit 24 and other molten metal is drawn up from the ladle through conduit 25. While being transferred and moved in the vacuum vessel, the molten metal is degasified. The centrifugal force causes the molten metal introduced into the vacuum vessel 7 to form a somewhat paraboloidal shape having a central recess at the upper side as indicated in FIG. 1, because decreasing temperature and decreasing gas content in the course of degasification produce a gradient of pressure progressively increasing from the central toward the peripheral portions of the molten metal within the vacuum vessel 7, so that degasified molten metal flows down from the openings adjacent the peripheral walls of the vessel through the discharge conduit 24. Since the centrifugal force arising from the rotation of the vacuum vessel 7 causes forced unilateral motion of molten metal, smooth circulation of molten metal is attained between the ladle the vacuum vessel through the drawup end discharge conduits. In order to avoid repeated drawing-up of degasified molten metal into the vacuum vessel to attain efiicient degasification of the entire molten 4 metal contained in the ladle ,it is preferable to vertically space apart as far as possible the opening of the discharge conduit with respect to the openings of the drawup conduits within the ladle. With the vacuum degasifying apparatus as described hereinbefore, it is possible to C11- culate molten metal at a desired circulation speed since increasing the r.p.m. of the vacuum vessel produces increased pressure gradient occurring in the drawn-up molten metal. Also, the degree of degasification may be suitably controlled to meet the required quality of th products. Further, if it is intended to carry out alloying process simultaneously with the degasifying treatment, it may be accomplished by appropriately operating the valve 28 to spatter filling material contained in the hopper 19 on the drawn-up molten metal, or by flowing up inert gaS such as argon through the frictional seal mechanism 17, pipe 23 and hole 26 into the drawn-up molten metal, so as to create a desired alloy structure.

When molten metal contained in the ladle 4 has undergone a desired degasifying treatment, the operation of the vacuum pump and the motor is stopped, the piston-cylinder assemblies are reversely operated to lower the movable floor member 5 to a position where the rails 2 are in alignment with the rails on the stationary floor, and the carriage 1 is replaced with a new one supporting another ladle containing a fresh charge of molten metal.

As has been apparent from the foregoing description according to the invention the vacuum vessel is rotated about a vertical axis to admit there molten metal through the openings located substantially at the center of its bottom and discharge degasified molten metal through the openings adjacent its peripheral walls, whereby use of argon gas may be dispensed with, smooth circulation of molten metal is attained, and the speed of forced circulation of molten metal may be controlled by regulating r.p.m. of the vacuum vessel.

Further, with the position of the opening of the discharge conduit below the openings of the draw-up conduits within the ladle, degasified molten metal coming out of the discharge conduit can directly settle on the bottom of the ladle because of its greater specific gravity owing to its reduced temperature after degasification and to its reduced gas content without passing through lighter undegasified charge which is in turn conveniently drawn up without being mixed with already treated charge under otherwise occurrable convection due to heavier degasified charge, which contributes to the efficiency of operation of the apparatus.

Moreover, as the molten metal within the vacuum vessel is forced to move at substantially the same angular velocity as that of the vacuum vessel, wear of the refractory lining of the vacuum vessel by friction with molten metal is extremely small to elongate the service life of the apparatus.

What is claimed is:

1. continuous molten metal degasifying apparatus COmpllSlIlg,

,(a) means for conveying a ladle below a vacuum vessel at a workstation;

(b) a vacuum vessel at said workstation, disposed so as to be above said ladle, including a frame structure for rotatably supporting said vacuum vessel for rotation about a vertical axis, said vacuum vessel having a bottom member secured to a concave bottom Sectron;

(c) a cylindrical tail extending downwards from said bottom section center, concentric with the axis of rotation of said vacuum vessel;

(d) at least one elongated molten metal draw-up conduit defined by said tail, the upper end thereof communicating with the center portion of the bottom member to the interior of said vacuum vessel, said draw-up conduit extending at the lower end thereof in close proximity to said axis of rotation along the outer wall of said tail, the lower opening of the draw-up conduit being substantially above the bottom of said tail, the upper opening of the draw-up conduit being substantially along the axis of rotation of said bottom section;

(e) at least one discharge conduit whose upper end is disposed in the interior of said vacuum vessel along the peripheral wall thereof said conduit extending then inwardly to said tail and passing to the bottom of said tail substantially along said axis of rotation of said vessel within said tail; and,

(f) means to rotate said vacuum vessel and means to exhaust said vacuum vessel.

6 References Cited 7/1960 France. 8/1960 France.

J. SPENCER OVERHOLSER, Primary Examiner 10 ROBERT D. BALDWIN, Assistant Examiner US. Cl. X.R. 

